1. Field of the Invention
The present invention relates to space light modulating technology for use in a projector, display unit, printing and the like, and more particularly to a hologram color filter, production method of the hologram color filter and space light modulating apparatus using the hologram color filter.
2. Description of the Related Art
A space light modulating apparatus using the hologram color filter such as a color display unit has such an advantage in that its use efficiency of light is higher as compared to the color display unit using an ordinary color filter. For example, Japanese Patent Application Laid-Open No.2-500937 has disclosed a color display unit and method thereof using the hologram lens, in which the hologram lenses for red(R), green(G) and blue(B) are arranged horizontally in line in front of a stripe target such that they are disposed on multiple vertical stages so as to form each focal point on a target plane through each of the lenses thereby ensuring a high reading light efficiency.
Further, the Japanese Patent Application Laid-Open No.9-189809 (Japanese Patent Application No.7-315956) has disclosed a projection type display apparatus provided with a space light modulating unit which divides an incident light by diffraction to plural light beams having different wavelength bands as a color separating means and selectively collects light of each wavelength band at a picture element position of a corresponding color.
In the space light modulating unit employed in this conventional projection type display apparatus, its hologram color filter has such a characteristic that the diffraction efficiency of one polarized wave (hereinafter referred to as first polarized wave) of S polarized wave and P polarized wave with respect to a light impinging at a predetermined incident angle is kept substantially maximum while a difference of the diffraction efficiency between the first polarized wave and other polarized wave (hereinafter referred to as second polarized wave) is more than 30%. Of lights impinging upon this hologram color filter, the first polarized wave is diffracted by the hologram color filter and divided to spectrum, and then selectively converged to a picture element electrode position of a corresponding color on the liquid crystal display. The lights converged selectively to each picture element electrode is subjected to light modulation relating to video signal of a corresponding color, reflected and impinges again upon the hologram color filter. Then, the hologram color filter projects a polarized wave passing therethrough without being diffracted to a screen in an enlarged size.
A conventional space light modulating apparatus using the hologram color filter will be described more in detail with reference to FIG. 1.
The hologram color filter 1 comprises three layers of a hologram lens 1B for blue (B), a hologram lens 1G for green (G) and a hologram lens 1R for red (R). White light emitted from a xenon lamp or a metal-halide lamp (not shown) impinges upon the hologram lens 1B of the top layer of the hologram color filter 1. Here, only the B component is diffracted, and then focused and impinges upon the space light modulating element 3 constituted of a LCD panel by an operation of the lens. The G and R lights not diffracted by the hologram lens 1B for B advance straight in the hologram lens 1B for B and impinges upon the hologram lens 1G for G. Then, only the G component is diffracted and focused and impinges upon the space light modulating element 3 by an operation of the lens. Then, the R light not diffracted by the hologram lens 1G for G advances straight in the hologram lens 1G for G and then impinges upon the hologram lens 1R for R. Here, this light is diffracted and focused and impinges upon the space light modulating element 3 by an operation of the lens.
The space light modulating element 3 is constituted of a transparent electrode layer 4, picture element electrode layer 5 and liquid crystal 6 which is disposed therebetween and sealed such that it is sandwiched by an orientation film (not shown). A plurality of the picture element electrode layers 5 are provided for each of R, G and B so that they are driven by the R, G, B picture element signals. Then, the B light converged by the hologram lens 1B for B impinges upon the B picture element electrode 5B. The G light converged by the hologram lens 1G for G impinges upon the G picture element electrode 5G. The R light converged by the hologram lens 1R for R impinges upon the R picture element electrode 5R.
A voltage corresponding to a picture element signal is applied between the picture element electrode layer 5 and transparent electrode layer 4 of the incident side. Polarization and modulation corresponding to an extent of this voltage are executed on the incident light by the liquid crystal 6. For example, if a liquid crystal oriented vertically is used as the liquid crystal 6, a portion corresponding to a picture element signal of light impinging as S wave component becomes P wave component. Light after modulation is reflected by the picture element electrode layer 5 (or dielectric material mirror) and impinges upon the hologram color filter 1 again. The P wave component of this light passes through the hologram color filter 1 as it is. As a result, it comes that only a component corresponding to the picture element is taken out. By projecting this transmission light onto a screen, a picture is displayed. Meanwhile, most of the S wave component of the light impinging upon the hologram color filter 1 again is diffracted again, advances in an opposite direction to the incident light and returns to a light source. By providing a polarizer allowing the P wave component to pass in the output light path as required, the S wave component passing through the hologram color filter 1 can be cut off.
Next, a production method of the hologram color filter having three layers will be described with reference to FIGS. 2A-2D. First, an EB lattice 7 constructed in the form of a concave lens by electron beam (EB) as shown in FIG. 2A is used. The EB lattice 7 has a lattice construction having continuously differing pitches corresponding to the lens. A plurality of the lattices 7 are provided continuously on the surface of the glass substrate 8 so that the EB master (exposure master) 9 is formed as shown in FIG. 2B. A layer of hologram recording material 11 is formed on the surface of the other glass substrate 10 appropriately such that the hologram recording material 11 is disposed so as to oppose the EB master 9 in a condition that it is in contact with the EB master 9.
With this condition, exposure light 12 is irradiated from an exposure light source (not shown) at a predetermined angle as indicated by an arrow in FIG. 2B. Consequently, as shown in FIG. 2A, 0 order light L0 which advances straight and primary order light L1 diffracted by the lattice are obtained. Although a small amount of higher order light are produced as the diffracted light depending on the case, this matter is omitted in a following description to facilitate understanding. Because the hologram recording material 11 is disposed below the EB master as described above, interference pattern between the 0 order light L0 and primary order light L1 is formed. As a result, a refractivity distribution similar to the interference pattern, or a hologram lens is formed on the hologram recording material 11. As other production method, the reference light is used from an oblique direction as the 0 order light and the object wave is irradiated vertically as the primary order light so as to make both the lights interfere with each other.
To form a hologram color filter having three layers as shown in FIG. 1, first of all, the hologram recording material 11 is exposed by the EB master 9 for B so as to form a hologram lens 1B for B. Next, as shown in FIG. 2C, the hologram recording material 11 is provided on the hologram lens 1B for B. Then, an EB master 13 for G is disposed so as to oppose the hologram recording material 11 and the hologram recording material 11 is exposed so as to form a hologram lens 1G for G. Further, as shown in FIG. 2D, the hologram recording material 11 is provided on.the hologram lens 1G for G and an EB master 14 for R is disposed so as to oppose the hologram recording material 11 and the hologram recording material 11 is exposed so as to form a hologram lens 1R for R. By forming the three layers of the hologram recording material and repeating the exposure operation by the EB master for each layer three times, the hologram color filter 1 having the three layers is produced.
Although the thicknesses of the hologram lenses 1R, 1G, 1B for R, G, B are substantially the same, there is such a problem that light availability differs depending on color because the diffraction efficiency in each of the hologram lenses 1R, 1G, 1B differs depending on the wavelength of light or color of the light.
Further, the aforementioned Japanese Patent Application Laid-Open No.9-189809 has not mentioned a thickness of the thin plate glass layer provided on a reading light emission side of the hologram color filter formed by overlaying a plurality of the different hologram lenses relating to the three primary colors or carrying out multiple exposures to a single-layer hologram light sensitive film by a plurality of the hologram lenses.
That is, according to the structure shown in FIG. 1 of the aforementioned patent application(Japanese Patent Application No.7-315956), the emission lights from the hologram color filters 3 of three layers corresponding to the three primary colors are made to converge on each corresponding picture element electrode layer 13. Thus, the focal lengths of the hologram lens arrays 3r, 3g, 3b are set to be different such that the focal points of the hologram lens arrays 3r, 3g, 3b of each corresponding color exist on a same plane apart from the surface of the hologram color filter by each desired distance.
However, such a conventional art shown in FIG. 3 has a following problem. That is, because the same patent application has not mentioned particularly the thickness of the thin plate glass layer, if the sum thickness (t11+t12) of the thickness of the thin plate glass layer 21 and thickness of the adhesive agent layer 39 bonded to the reading light emission side of the hologram color filter 1 is larger than the shortest focal length L1 in glass of the hologram lenses 1R, 1G, 1B of corresponding colors, emission light from the thin plate glass layer 21 becomes radiant light, so that one color light on the picture element electrode 5R, 5G, 5B of the picture element electrode layer 5 is mixed with another color light adjacent thereto thereby inducing mixing of the colors shown in FIG. 4. Therefore, the reproductivity of colors is worsened.
There is another problem to solve. That is, when each hologram lens is formed, in FIG. 2B, if the exposure light 12 is irradiated to the hologram recording material 11 of each layer, a fringe pattern is formed thereon and by heat developing this, the refractivity change is intensified so as to produce a one-layer hologram lens. The refractivity change of the hologram recording material 11 depends on the space of the fringe pattern and inclination angle determined by the 0 order light (reference light) and primary order light (object light).
FIGS. 5 and 6 show this state and indicate a one-layer hologram lens 1B (1G, 1B) as a representative.
If the reference light 15 is irradiated obliquely to the hologram recording material 11 and the object light 16 is irradiated thereto vertically as shown in FIG. 5, the fringe pattern 17 of the angle xcex1 is formed in an oblique direction. These lights correspond to the 0 order light and primary order light as described above. The direction of this fringe pattern 17 is a direction for dividing an intersection angle xcex8 between the reference light 15 and object light 16 to two parts. The angles xcex81, xcex82 formed by the direction of the fringe pattern 17 and directions of both the lights 15, 16 are such that xcex81=xcex82 or they are of the same angle.
As described above, the hologram recording material 11 in which the fringe pattern 17 is formed is subjected to heat development treatment by adding heat to intensify the refractivity change. As a result, the fringe pattern 17 rises at a slight angle xcex94xcex1 as shown in FIG. 6 so as to increase the inclination angle. This phenomenon is called fringe rotation. If this fringe rotation occurs when the maximum efficiency is desired to be obtained, when the reproduction light 18 is projected to the hologram lens 1B(1G, 1R) from an oblique direction of a predetermined angle, sometimes the diffracted light 18A is emitted in a direction deviated at a slight angle xcex94xcex8 from vertically downward although this light is set to be emitted vertically downward in the same Figure. Therefore, it comes that this diffracted light 18A does not reach a desired picture element.
Accordingly, the present invention has been made to solve such a problem of the conventional art and therefore, an object of the invention is to provide a hologram color filter capable of improving light availability and a space light modulating apparatus using the same.
Another object of the invention is to provide a production method of a hologram color filter capable of emitting a diffracted light in a desired direction at an optimum efficiency by compensating for a fringe rotation and a space light modulating apparatus using a filter produced according to the same method.
Still another object of the invention is to provide a hologram color filter suitable for achieving a projection type display unit excellent in reproduction of color without mixing of colors.
To achieve the above object, there is provided a hologram color filter having two or more hologram lenses, wherein the thickness of each layer of the hologram lenses having two or more layers is smaller as the wavelength of light to be diffracted by each layer is shorter.
Because according to the present invention, the diffraction efficiency can be improved, the light availability can be also improved.
According to a preferred embodiment of the present invention, the thickness of each of the hologram lenses having two or more layers accurately corresponds to a ratio of the wavelength of light to be diffracted by each layer.
By using the aforementioned hologram color filter in a space light modulating apparatus, the light availability can be improved and further, a desired light can be emitted from a desired picture element.
Further, to achieve the above object, there is provided a space light modulating apparatus comprising: a hologram color filter formed by overlaying a plurality of different hologram lenses relating to the three primary colors or carrying out multiple exposures on a single layer hologram light sensitive film by the plurality of the hologram lenses, the hologram color filter diffracting incident white reading light to a plurality of light beams having each different wavelength and focusing each thereof onto a picture element electrode of each corresponding color; a thin plate glass layer provided in a firm contact with reading light emission side of the hologram color filter; and a space light modulating element for modulating light diffracted by the hologram color filter, the space light modulating apparatus being so constructed that the thickness of the thin plate glass layer is smaller than the shortest focal length of the focal lengths in glass of each of the plurality of the hologram lenses.
According to a preferred embodiment of the present invention, the thin plate glass layer is bonded to a reading light emission side surface of the hologram color filter via adhesive agent and a sum of the thickness of the adhesive agent and thickness of the thin plate glass layer is smaller than the shortest focal length of the focal lengths in glass of each of the plurality of the hologram lenses.
According to the present, invention, the distance between the hologram color filter and picture element electrode layer can be so adjusted that the three primary colors separated by the hologram color filter are converged onto each corresponding picture element properly and therefore, a space light modulating apparatus excellent in reproduction of color without mixing of colors can be achieved.
Further, to achieve the above object, there is provided a method for producing a hologram color filter comprising the steps of: forming a fringe pattern on a hologram recording material; creating a one-layer hologram lens by heat-development of the hologram recording material; providing a further hologram recording material on the one-layer hologram lens; and repeating the above procedure so as to create a multiple layer hologram lens, wherein the fringe pattern to be formed on the hologram recording material is formed at a recording angle for compensating for a fringe rotation such that light having a desired wavelength is emitted in a desired direction.
According to a preferred embodiment of the present invention, the desired direction is a normal direction of the hologram color filter.
According to this invention, the fringe pattern prior to heat development is formed in such a condition that it is rotated by an angle corresponding to the rotation angle of a fringe rotation in an opposite direction thereto. Therefore, the fringe pattern after heat development is formed in a desired direction as designed.
Further, by employing a hologram color filter produced according to the above method in the space light modulating apparatus, the diffracted light is emitted in a desired direction with a desired diffraction efficiency as designed, so that the diffracted light hits a desired picture element accurately.
The nature, principle and utility of the invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings.